Here are some ideas for optional creation rules I thought I'd share.
Armor Peircing Explosive shells
These shells are fired from guns, treat them as explosives with a cost double their size. The shells are treated as regular shots from the gun they are fired from, but when the shell fails to penetrate a surface, it explodes as an explosive.
For Example, say a size 3 shell is fired at an armored car. The use roll of 4 succeeds and the armored car's armor of 2d10 is rolled against the gun's 3d6 damage. The gun's totals 11, this exceeds the 9 rolled for the armored car. The shots leftover 2 damage is not enough to penetrate the other side of the car, so it explodes, 3d10 damage to the car's crew members. Basically, the shell works the same as any shot under the overkill rules, but when it finally fails to overcome the armor, it explodes.
Reactive armor is purchased just like armor plates, but adds d10 instead of d6 to the creation's armor roll. However, when reactive armor does this, it cannot be reused as it has detonated.
For most of you who don't know, reactive armor is explosives placed on tanks that detonate incoming explosives before they hit the tank's surface, reducing penetration capabilities.
Obviously these rules are somewhat biased towards vehicles, but I can't think of anything for living creations, though I suppose things such as reactive armor on dinosaurs are possible.